Multi-stage vacuum pump of the dry pump type

ABSTRACT

A multi-stage vacuum pump of the dry pump type is disclosed. The multi-stage vacuum pump includes a plurality of pumping stages each respectively having an inlet and an outlet, the pumping stages being mounted in series between a suction port and a discharge port of the vacuum pump, characterized in that the vacuum pump also includes at least one valve configured to dump pressure from a pumping stage, said valve being arranged in the upper part of the vacuum pump, on the same side as the inlet of the pumping stage.

The present invention relates to a multi-stage vacuum pump of the dry pump type. The invention notably applies to a dry vacuum pump comprising two shafts with rotary lobes of the “roots” or “claw” type, or even of the scroll or screw type or using another similar principle.

Multi-stage vacuum pumps comprise several pumping stages in series through which there circulates a gas that is to be pumped between a suction port and a discharge port. Among known vacuum pumps, a distinction is made between those that have rotary lobes which are also known by the name “roots” pumps, having two or three lobes and those with double claws, also known by the name of “claw” pumps. Pumps with rotary lobes comprise two rotors of identical profiles, rotating in opposite directions inside a stator. During the rotation, the gas that is to be pumped is trapped in the empty space comprised between the rotors and the stator, and is driven by the rotor toward the next stage or, after the last stage, to the discharge port outlet. Operation involves no mechanical contact between the rotors and the stator, and this means that there can be a complete absence of oil within the pumping stages.

In order to reduce the power consumption of the vacuum pump, the last pumping stages situated toward the discharge port end generally have a swept volume, which means to say a pumped gas volume, that is smaller than that of the first pumping stages, at the suction port end.

However, during certain applications, notably with a view to reducing the pressure in the chamber from atmospheric pressure, the vacuum pump has to absorb significant initial streams of gas that cannot be admitted by the last pumping stages at the discharge port end, thus creating significant pressure differences in the vacuum pump and leading to high power consumption. This is the case, for example, where pumping out a loading/unloading lock (“load lock”), where chambers are brought down from atmospheric pressure to an evacuated state cyclically (approximately every 12 seconds).

These pressure differences may also cause lubricants from the lubricated bearings to migrate towards the pumping stages. Now, it is absolutely essential that no traces of oil or grease find their way into the pumping stages for applications referred to as “dry”.

It is therefore one of the objects of the present invention to propose a vacuum pump of the dry pump type that is able to evacuate the surplus gas that occurs when the stream of gas to be pumped becomes too high for the capability of the vacuum pump, notably in order to prevent lubricant migrating toward the pumping stages and to limit the power consumption of the vacuum pump.

It is another object of the present invention to attenuate the vibrations of the rotary shafts that support the rotors of the vacuum pumps which may occur when pumping starts up, following the pressure surge that occurs when the isolating valve between the chamber to be pumped out, that is at atmospheric pressure, and the vacuum line that is at low pressure, is opened.

It is another object of the present invention to limit the heating of the vacuum pump that may also occur during this initial evacuation phase.

To this end, one subject of the invention is a multi-stage vacuum pump of the dry pump type comprising a plurality of pumping stages respectively comprising an inlet and an outlet, the pumping stages being mounted in series between a suction port and a discharge port of the vacuum pump, characterized in that the vacuum pump further comprises at least one valve configured to dump pressure from a pumping stage, said valve being arranged in the upper part of the vacuum pump, on the same side as the inlet of the pumping stage.

The valve, in the sense of pressure release valve, (or “clapet” in French), (or “exhaust valve”) makes it possible to reduce the significant pressure differences in the pumping stages. The seals fitted between the lubricated bearings and the pumping stages are thus protected. Their premature wear and therefore the risk of lubricant migrating toward the pumping stages are limited. Moreover, by reducing the pressure differences in the pumping stages, the heating of the vacuum pump and its power consumption are limited.

Furthermore, the valve is arranged in the upper part of the vacuum pump at the same side as the inlet of the pumping stage, and that offers several advantages.

The valve, for example, comprises at least one passage formed in the casing of the vacuum pump connecting a central housing of a pumping stage and opening via a mouth that can be closed off by a respective mobile shutter (or “mobile obturator”) of the valve.

One first advantage lies in the fact that manufacture of the vacuum pump casing becomes simpler because there is no need to machine cavities in the casing under the pumping stages to accept the lifted mobile shutters of the valve. All that is actually required is the creation of a passage in the upper part of the stator.

In addition to making the vacuum pump easier to produce, more space becomes available in which to situate the valve.

Moreover, surplus gas is easily exhausted to the outside via the passage. In effect, this prevents the gas that is to be dumped passing along various narrow and sinuous paths which reduce conductance, slow and heat the gas, causing heating of the vacuum pump that can sometimes be significant.

According to another aspect of the invention, at least two pumping stages comprise a respective valve.

Thus, the vacuum pump comprises one or several first valve/s arranged in the upper part of the vacuum pump on the same side as the inlets to the pumping stages and one or more second valve/s arranged in the lower part of the vacuum pump on the same side as the outlets of the pumping stages.

By arranging the valves at the top or at the bottom of the vacuum pump, it is possible to get around problems of space required. Thus, for example, two pumping stages can have pressure dumped from the bottom, and two pumping stages from the top, in order to solve the problems of space in the vacuum pump.

According to another aspect of the invention, all the pumping stages comprise a respective valve. Thus, all the stages can exhaust the surplus gas simultaneously, without passing through the next pumping stage, and autonomously. By exhausting all the pumping stages of the vacuum pump simultaneously, surges of the flow of gas in the pumping stages are significantly reduced, these being what cause the vibrations of the rotary shafts that may occur notably at the moment of opening of the isolating valve that separates the chamber that is to be pumped out from the low-pressure vacuum line connected to the vacuum pump.

According to one embodiment, the vacuum pump comprises a case fixed to the upper part of the casing of the vacuum pump, covering the valves and connecting the mouths of the passages of the valves toward a common outlet. It is thus possible to control the exhausting of the dumped gases, for example toward the discharge port of the vacuum pump.

Another subject of the invention is a multi-stage vacuum pump of the dry pump type comprising a plurality of pumping stages respectively comprising an inlet and an outlet, the pumping stages being mounted in series between a suction port and a discharge port of the vacuum pump, characterized in that the vacuum pump further comprises at least two valves configured to dump pressure from a respective pumping stage, the valve comprising at least one passage formed in the casing of the vacuum pump connecting a central housing of a pumping stage and opening via a mouth that can be closed off by a respective mobile shutter of the valve, the mobile shutter being chosen from a flat disk and a diaphragm.

Yet another object of the invention is a multi-stage vacuum pump of the dry pump type comprising a plurality of pumping stages respectively comprising an inlet and an outlet, the pumping stages being mounted in series between a suction port and a discharge port of the vacuum pump, characterized in that the vacuum pump comprises as many valves respectively configured to dump pressure from a pumping stage as there are pumping stages, so as to dump pressure from all of the pumping stages.

Other features and advantages of the invention will become apparent from the following description given by way of nonlimiting example, with reference to the attached drawings in which:

FIG. 1 is a perspective view of a first example of a multi-stage vacuum pump,

FIG. 2 a depicts a schematic view in cross section of a multi-stage vacuum pump with a valve according to the first example in the closed position,

FIG. 2 b depicts a view similar to FIG. 2 a, with the valve in the open position,

FIG. 3 depicts a schematic view of a second example of a multi-stage vacuum pump,

FIG. 4 a depicts another example of valve,

FIG. 4 b depicts another example of valve,

FIG. 4 c depicts another example of valve,

FIG. 5 a depicts a simplified schematic view of a multi-stage vacuum pump according to a third embodiment, which has as many valves as there are pumping stages, the valves being in the closed position, and

FIG. 5 b depicts a view similar to FIG. 5 a with the valves in the open position.

In these figures, elements that are identical bear the same reference numerals.

FIGS. 1, 2 a and 2 b illustrate a first embodiment of a multi-stage vacuum pump of the dry pump type 1. As has been depicted schematically in FIG. 2 a, the vacuum pump comprises two rotary shafts 2 bearing rotary lobed rotors 3 of the “roots” type. Of course, the invention also applies to other types of multi-stage vacuum pump of the dry pump type, such as “claw” pumps, scroll pumps, screw pumps or pumps using another similar principle.

As can be seen in the schematic view of FIG. 3, the multi-stage vacuum pump 1 comprises several pumping stages, six in this example, TA, T1, T2, T3, T4, TR, mounted in series between a suction port 4 and a discharge port 5 of the vacuum pump 1 and through which a gas that is to be pumped can circulate. On the inside, the rotary shafts 2 extend through the pumping stages TA, T1, T2, T3, T4, TR in the form of rotary-lobed rotors 3 and are driven from the side of the discharge port TR by a motor M of the vacuum pump 1 (FIG. 1).

The rotors have identical profiles, rotating in a central housing 10 inside the casing 6 in opposite directions. As they rotate, the gas that is to be pumped is trapped in the empty space comprised between the rotors 3 and the casing 6, and is driven by the rotors 3 toward the next stage or toward the discharge port 5 after the last pumping stage TR. The vacuum pump 1 is referred to as a “dry” pump because, in operation, the rotors 3 rotate inside the casing 6 of the vacuum pump 1 in opposite directions, with no mechanical contact between the rotors 3 and the casing 6, allowing a complete absence of oil.

Each pumping stage TA, T1, T2, T3, T4, TR comprises a respective inlet 7 and a respective outlet 8 (FIG. 2 a). The successive pumping stages TA, T1, T2, T3, T4, TR are connected in series one after the other by respective inter-stage pipes 9 that connect the outlet 8 of the preceding pumping stage to the inlet 7 of the next stage (FIG. 3). The first pumping stage TA, the inlet 7 of which communicates with the suction port 4 of the vacuum pump 1 is also referred to as the “suction stage”. The last pumping stage TR, the outlet 8 of which communicates with the discharge port 5 of the vacuum pump 1 is also referred to as the “discharge stage”. The pumping stages T1, T2, T3 and T4 mounted in series between the suction stage TA and the discharge stage TR are also referred to as intermediate stages. The pumping stages have a swept volume, i.e. a pumped gas volume, that decreases between the suction stage TA and the discharge stage TR.

The inlets 7 of the pumping stages TA, T1, T2, T3, T4, TR are arranged in the upper part of the casing 6 of the vacuum pump 1 and the outlets 8 are arranged in the lower part of the casing 6 of the vacuum pump 1. In operation, the gases are driven by the rotors 3 in the central housing 10 from the inlet 7 toward the outlet 8 then go up in the inter-stage pipe 9 toward the inlet 7 arranged in the upper part of the next pumping stage.

The vacuum pump 1 comprises at least one valve configured to dump pressure from (or “délester” in French), (or to “unballast”), a pumping stage in order to absorb the large streams of gas that arise notably when starting to evacuate a chamber at atmospheric pressure that is connected to the suction port 4 of the vacuum pump.

By reducing the significant pressure differences in the pumping stages, the seals fitted between the lubricated bearings and the pumping stages are protected. Thus, their premature wear and therefore the risks of lubricant migrating to the pumping stages are limited. Moreover, by reducing the pressure differences in the pumping stages, the heating of the vacuum pump and its power consumption are also limited.

The valve comprises at least one passage 11 and at least one mobile shutter for closing off the respective passage (FIGS. 2 a and 2 b). The passage 11 is formed in the casing 6, and connects the central housing 10 of a pumping stage to the outside, for example to the discharge port 5 of the vacuum pump 1.

The valve is a passive dump module, able to adopt an open or closed position according to the overpressure in the pumping stage, the open or closed position being dependent on the pressure difference between the upstream and downstream sides of the valve. In the closed position, when the pressure difference between the upstream and downstream sides of the valve is below a valve calibration threshold, the mobile shutter closes off the passage 11 in a fluidtight manner. In the open position, when the pressure difference between the upstream and downstream sides of the valve is above the valve calibration threshold, the surplus gas can be exhausted from the pumping stage directly to the outside, bypassing the next pumping stages.

In a first embodiment of the valve depicted in FIGS. 1, 2 a and 2 b, the mobile shutter comprises a ball 12 and the passage 11 has a frustoconical mouth 13 forming a seat for the ball 12.

The ball 12 is, for example, made of steel. The frustoconical mouth 13 or the ball 12 may have a coating, for example, an elastomeric coating, such as one made of silicone, which improves their mechanical integrity and their resistance to the high temperatures of the heated pump.

In the closed position, the frustoconical mouth 13 of the passage 11 is closed by the ball 2 which rests on the seat of the passage 11 (FIG. 2 a). When resting against the seat, the ball 12 closes the frustoconical mouth 13 of the passage 11 in a fluidtight manner. In the event of overpressure in the pumping stage, the ball 12 lifts from the seat, opening the mouth 13 of the passage 11 (FIG. 2 b). The frustoconically shaped mouth 13 also automatically centers the ball 12 and cushions its fall back down onto the seat.

According to a second embodiment of the valve depicted in the example of FIG. 4 a, the mobile shutter is formed by a flat disk 17 that in a fluidtight manner closes off the passage 11 depending on the pressure.

The valve may comprise a spring 18 which urges the mobile shutter 17 against the mouth of the passage 11 to close it (FIG. 4 a). In the event of an overpressure in the pumping stage, the mobile shutter 17 lifts, opening the mouth of the passage 11.

According to another embodiment of the valve, the mobile shutter comprises for example a ball and a spring is arranged between the shutter and the mouth of the passage 11 (not depicted).

According to yet another embodiment of the valve, the mobile shutter comprises a diaphragm 19 (FIG. 4 b). In the closed position, the diaphragm 19 closes the mouth of the passage 11 (see dotted lines in FIG. 4 b). In the open position, the diaphragm 19 is deformed by the overpressure gas, opening the mouth of the passage 11 (FIG. 4 b).

According to a third embodiment depicted in FIG. 4 c, the valve comprises a poppet valve, like a motor vehicle engine poppet valve. The poppet valves comprise a head 20, a collar 21 and a stem 22. The valve head 20 of circular shape, acts as the mobile shutter that closes off the passage 11. When the valve is in the closed position, the head 20 presses against the valve seat formed by the mouth of the passage 11 to provide sealing and correct centering of the valve. That part of the head 20 that is in contact with the seat may have a frustoconical shape that complements a frustoconical shape of the mouth of the passage 11 (not depicted). The stem 22 provides the vertical guidance of the valve in the passage 11.

Provision may also be made for the valve to comprise two passages bypassing one another, and two respective mobile shutters rather than just one (not depicted). Two set ups bypassing one another are then used to dump a significant stream of gas, maintaining a compact layout.

In the first embodiment depicted in FIGS. 1, 2 a and 2 b, the valve is arranged in the upper part of the vacuum pump 1, on the same side as the inlet 7 of the pumping stage. Thus, in the event of overpressure in the pumping stage, for example when evacuation begins, the valve allows the surplus gas to be exhausted from the top rather than from the bottom and this offers several advantages.

First, the manufacture of the casing 6 of the vacuum pump is simplified because there is no need to machine cavities in the casing 6 under the pumping stages TA, T1, T2, T3, T4, TR in order to accept the lifted mobile shutters of the valve. Indeed, all that is required is the creation of a passage 10 in the upper part of the stator 6. Furthermore, the assembly can be kept in a fluidtight manner by a case 15 to ensure the path followed by the dumped gases, for example, toward the discharge port 5 of the vacuum pump 1.

In addition to making the vacuum pump easier to produce, more space is available for positioning the valve.

Moreover, the surplus gas can easily be exhausted to the outside by the passage 10. This then prevents the dumped gas from following various narrow and sinuous paths which reduce conductance, slow and heat the gas, causing heating of the vacuum pump that can sometimes be significant.

In the second embodiment of FIG. 3, provision is made for at least two pumping stages to comprise a respective valve.

According to a first example, one or more first valve/s 23 are arranged in the upper part of the vacuum pump on the same side as the inlets 7 of the pumping stages TA, T1, T2, T3, T4, TR and one or more second valve/s 24 are arranged in the lower part of the vacuum pump on the same side as the outlets 8 of the pumping stages TA, T1, T2, T3, T4, TR.

For example, provision is made for the pumping stages on the suction side, which have the largest swept volumes, to comprise a respective valve for dumping the surplus gas.

Thus, in the example depicted, two first valves 23 are arranged in the upper part of the vacuum pump on the same side as the inlets 7 of the two first pumping stages TA, T1 and two second valves 24 are arranged in the lower part of the vacuum pump on the same side as the outlets 8 of the pumping stages T2, T3. The two first valves 23 and the two second valves 24 are consecutive in this example.

By having the choice as to whether to position the valves at the top or at the bottom of the vacuum pump it is possible to best suit the space available in the vacuum pump.

According to a second example, the valves 23 are all arranged in the upper part of the vacuum pump on the same side as the inlets 7 of the pumping stages TA, T1, T2, T3, T4, TR or all arranged in the lower part of the vacuum pump on the same side as the outlets 8 of the pumping stages TA, T1, T2, T3, T4, TR (this is not depicted).

FIGS. 5 a and 5 b depict another embodiment in which all the pumping stages TA, T1, T2, T3, T4, TR comprise a respective valve.

The vacuum pump comprises, for example, a case 15 fixed to the upper part of the casing 6 of the vacuum pump 1 covering the valves and connecting the passages 11 to a common outlet 16. The common outlet 16 is, for example, connected to the discharge port 5 of the vacuum pump. The case 15 is thus arranged on top of the mobile shutters. It is fixed to the casing 6 by conventional means of attachment. It is, for example, made of a single piece, as a casting like the casing 6 of the vacuum pump 1.

During normal operation of the vacuum pump 1, namely for pumping a stream of gas that suits the pumping capability of the vacuum pump 1, the mouths 13 are closed (FIG. 5 a). The mobile shutters, depicted schematically as balls 12 in FIGS. 5 a and 5, resting in the mouths 13 prevent the pumped gas from bypassing the next pumping stages. The pumped gas follows the path depicted by the dotted arrows in FIG. 3 a: the gas to be pumped is sucked in by the six pumping stages TA, T1, T2, T3, T4, TR and leaves from the discharge port 5 of the vacuum pump 1.

When there is a surplus of gas, namely when the stream of gas becomes too great for the pumping capability of the vacuum pump 1, for example, when pumping out from atmospheric pressure, the surplus gas lifts the balls 12 off their respective seat, uncovering the mouths 13 of the passage 11. The gas is then exhausted from the pumping stages TA, T1, T2, T3, T4, TR to the common outlet 16.

Then, as the stream of gas diminishes and can be handled by the vacuum pump 1, the balls 12 drop back down onto the mouths 13 which guide them into the center, cushioning their fall.

Thus, all the pumping stages TA, T1, T2, T3, T4, TR are able to exhaust surplus gas simultaneously, without this passing through the next pumping stage, and can do so autonomously.

By exhausting from all of the pumping stages TA, T1, T2, T3, T4, TR of the vacuum pump simultaneously, gas flow surges through the pumping stages, that cause the vibrations of the rotary shafts 2 that may arise notably at the time of opening of the isolating valve that separates the chamber to be pumped from the low-pressure vacuum line connected to the vacuum pump, are significantly reduced.

Although FIGS. 5 a and 5 b depict a multi-stage vacuum pump in which all the pumping stages have gas dumped from the top, on the same side as the inlets of the pumping stages, other embodiments can be produced for dumping gas from all the pumping stages.

For example, all the pumping stages may have gas dumped from the bottom, on the same side as the discharge port of the pumping stages.

Equally, certain pumping stages can have gas dumped from the top on the same side as the suction port of the pumping stages and others from the bottom on the same side as the discharge port of the pumping stages. 

1. A multi-stage vacuum pump of the dry pump type comprising: a plurality of pumping stages respectively comprising: an inlet; and an outlet; wherein the pumping stages are mounted in series between a suction port and a discharge port of the vacuum pump; wherein the vacuum pump further comprises at least one valve configured to dump pressure from a pumping stage, said valve being arranged in the upper part of the vacuum pump, on the same side as the inlet of the pumping stage.
 2. The vacuum pump according to claim 1, wherein at least two pumping stages comprise a respective valve.
 3. The vacuum pump according to claim 1, wherein all the pumping stages comprise a respective valve.
 4. The vacuum pump according to claim 1, wherein the vacuum pump comprises at least one first valve arranged in the upper part of the vacuum pump on the same side as the inlets of the pumping stages and at least one second valve arranged in the lower part of the vacuum pump on the same side as the outlets of the pumping stages.
 5. The vacuum pump according to claim 1, wherein the at least one valve comprises at least one passage formed in the casing of the vacuum pump and connecting a central housing of a pumping stage and opening via a mouth that can be closed off by a respective mobile shutter of the valve.
 6. The vacuum pump according to claim 5, wherein the mouth is frustoconical.
 7. The vacuum pump according to claim 5, wherein the mobile shutter is chosen from a ball, a flat disk and a diaphragm.
 8. The vacuum pump according to claim 1, characterized in that the at least one valve comprises a spring.
 9. The vacuum pump according to claim 1, wherein the vacuum pump comprises a case fixed to the upper part of the casing of the vacuum pump, covering the valves and connecting the mouths of the passages of the valves to a common outlet.
 10. A multi-stage vacuum pump of the dry pump type comprising: a plurality of pumping stages respectively comprising: an inlet; an outlet; wherein the pumping stages are mounted in series between a suction port and a discharge port of the vacuum pump; wherein the vacuum pump further comprises at least two valves configured to dump pressure from a respective pumping stage, the at least two valves respectively comprising at least one passage formed in the casing of the vacuum pump connecting a central housing of a pumping stage and opening via a mouth that can be closed off by a respective mobile shutter of the valve, the mobile shutter being chosen from a flat disk and a diaphragm.
 11. A multi-stage vacuum pump of the dry pump type comprising: a plurality of pumping stages respectively comprising: an inlet; and an outlet; wherein the pumping stages are mounted in series between a suction port and a discharge port of the vacuum pump; wherein the vacuum pump comprises as many valves respectively configured to dump pressure from a pumping stage as there are pumping stages, so as to dump pressure from all of the pumping stages. 